1. Technical Field
The present invention relates to an optical module and an atomic oscillator.
2. Related Art
In recent years, an atomic oscillator using Coherent Population Trapping (CPT) as a quantum interference effect has been proposed, and a reduction in size and a reduction in power consumption are expected. An atomic oscillator using CPT: uses a phenomenon known as Electromagnetically Induced Transparency (EIT) in which when two resonant lights that have different wavelengths (frequency) are simultaneously irradiated onto an alkali metal atom, absorption of the two resonant lights is stopped. For example, JP-A-2009-89116 discloses an atomic oscillator using CPT, and includes an optical module including a light source to emit coherent light, a gas cell in which alkali metal atoms are sealed, and a light-receiving element to detect the intensity of the light passing through the gas cell.
In an atomic oscillator using CPT, for example, a semiconductor laser can be used as a light source. In an atomic oscillator using a semiconductor laser as the light source, for example, a drive current of the semiconductor laser is modulated to generate sideband waves in the light emitted from the semiconductor laser, and the EIT phenomenon is caused.
However, the light emitted from the semiconductor laser in which the drive current is modulated includes not only the sideband waves, but also a fundamental wave (carrier wave) having a center wavelength which does not contribute to the EIT phenomenon. When the fundamental wave is irradiated onto the alkali metal atom, the wavelength (frequency) of light absorbed by the alkali metal atom is changed (known as the AC Stark effect) so that the frequency stability of the atomic oscillator is lowered.